Monitoring apparatus for monitoring the density of a material carried by a fluid and the flow of the fluid

ABSTRACT

An improved monitoring apparatus for sensing the density of a material carried by a fluid in a conduit and the flow of the fluid to activate a warning device when the density of the material or flow of the fluid drops below a predetermined level. Such an improved monitoring apparatus includes means for sensing the density of the material carried by said fluid and is adapted to provide a signal proportional to the density to a circuit means and means for sensing the flow of the fluid for providing a signal dependent on the flow to the circuit means. The circuit means is adapted to receive these signals and is operable to activate the warning device when either signal drops below a predetermined level. The means for sensing provides light to the conduit, a first sensor means for detecting the light intensity and a second sensor for sensing the amount of light reflected by the material.

0 l Unite States [72] Inventor Joseph A. Livers Roseville, Mich. [21]Appl. No. 820,493 [22] Filed Apr. 30, 1969 [45] Patented Nov.2,l.971[73] Assignee Eaton Yale & Towne Inc.

Cleveland, Ohio [54] MONITORING APPARATUS FOR MONITORING THE DENSITY OFA MATERIAL CARRIED BY A FLUID AND THE FLOW OF THE FLUID 18 Claims, 4Drawing Figs.

[52] U.S. Cl 340/236, 73/204, 250/218, 340/239, 356/103, 356/208 [51]Int. Cl ..G08b19/00 [50] Field oi Search 340/236, 239, 243; 73/204;356/102, 103, 104, 207, 208; 250/218 [56] References Cited UNITED STATESPATENTS 2,791,932 5/1957 Hall 356/207X 3,358,148 12/1967 Conklin et a1.356/104 Primary Examiner-John W. Caldwell Assistant Examiner- DanielMyer Alt0rneyY0unt & Tarolli ABSTRACT: An improved monitoring apparatusfor sensing the density ofa material carried by a fluid in a conduit andthe flow of the fluid to activate a warning device when the density ofthe material or flow of the fluid drops below a predetermined level.Such an improved monitoring apparatus includes means for sensing thedensity of the material carried by said fluid and is adapted to providea signal proportional to the density to a circuit means and means forsensing the flow of the fluid for providing a signal dependent on theflow to the circuit means. The circuit means is adapted to receive thesesignals and is operable to activate the warning device when eithersignal drops below a predetermined] level. The means for sensingprovides light to the conduit, 2 first sensor means for detecting thelight intensity and a second sensor for sensing the amount of lightreflected by the material,

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A! TTORA/E V3 MONITORING APPARATUS FOR MONITORING TllllE DENSITY OF AMATERIAL CARRIED BY A lFlLUIll) AND Til-IE FLOW OF Til-IE lFlLlUllD 'Thepresent invention relates to a monitoring apparatus which activates awarning device when the flow of a fluid in a conduit or the density of amaterial carried by the fluid drops below a predetermined level, andmore particularly to such a monitoring apparatus which includes adensity sensor which detects the amount of material carried by the fluidby measuring the amount of light reflected by the material carried bythe fluid.

Many various bearing surfaces require some type of constant lubrication.Typically, such lubrication is supplied by an oil-misting device. Theseoil-misting devices provide a material such as a lubricant oil insuspension in a fluid such as air and provide for flow of the materialcarried by the fluid to the bearing. It is apparent from such an examplethat the amount of the oil carried by the air must be sensed to assureproper lubrication of the bearings and on the other hand, the flow ofthe fluid must be sensed to assure continuous lubrication of thebearings.

Monitoring apparatuses for monitoring the density of the materialcarried by the fluid are known. These prior art devices are subject tovarious system fluctuations and do not provide for proper compensationfor these variables. In addition, these prior art devices do not providefor sensing the flow of the fluid to assure that the bearing will becontinuously lubricated.

The monitoring apparatus of the present invention provides a warningsignal if either the density of the material carried by the fluid or theflow of the fluid drops below a predetermined level. ln order to providean accurate measurement of the density, the density of the material issensed by the amount oflight reflected by the material. The two sensorsare provided such that intensity variations of the light source arecompensated and the difference in the signals created by these sensorsprovides measurement of the density. In addition such a differentialmeasurement increases the range of this differential signal and thus hasincreased accuracy.

The present invention also provides a density indicator which gives avisible indication of the amount of the density and a flow indicatorwhich gives a visible indication of the flow of the fluid at any givetime. Thus, when a warning device is activated, the area of difficultymay be readily determined.

Accordingly, it is an object of this invention to provide a monitoringapparatus which senses the density of a material carried in a fluid andthe flow of the fluid to actuate a warning device when the density or.the flow drop below a predetermined level. i

It is yet another object in the present invention to provide amonitoring apparatus which senses the density of a material carried in afluid by sensing the amount of light reflected by the material.

It is yet another object of the present invention to provide a sensor todetect the density of a material carried in a fluid by sensing theamount oflight reflected by the material.

It is yet another object in the present invention to provide a lightsource whose intensity is detected by a first sensor and the amount oflight reflected by the material carried by the fluid detected by asecond sensor wherein each ofthe sensors provide a circuit means with asignal wherein the signal from the second sensor when reduced by thesignal from the first sensor is proportional to the density and aflow-sensing means which detects the flow of the fluid and provides thecircuit means with a signal thereof wherein the circuit means is adaptedto actuate a warning device when the density of the material carried bythe fluid or the flow of the fluid drops below a predetermined level.

Yet another object of the present invention is to provide a monitoringapparatus having a density meter to give a visible indication ofthedensity of the material carried by the fluid.

A further object of the present invention is to provide a monitoringapparatus having a flow indicator to provide a visible indication oftheflow ofthe fluid.

Still further objects, advantages, and features of the present inventionwill be apparent to those skilled in the art to which it relates fromthe following detailed description made with reference to theaccompanying drawings forming a part of the specification and in which:

FIG. I is a schematic illustration of a mist supply and a monitoringapparatus of the present invention;

FlG. 2 is a cross-sectional view of the density sensor taken along lines2-2 of FIG. 1;

FIG. 3 is a cross-sectional view similar to F 1G. 2 of a secondembodiment of a density sensor; and

FIG. 4 is a schematic diagram showing the circuitry of the presentinvention.

The present invention provides a monitoring apparatus to give a warningsignal when either the density of a material carried by a fluid or theflow of the fluid drop below a predetermined level. A monitoringapparatus of the present invention includes a density sensor whichdetermines the density of the material be sensing the amount of lightreflected thereby and compensates for the intensity of the light source.

FIG. 1 shows a representative monitoring system l0 having a mist supply12 adapted to provide an oil mist. The oil material is suspended in afluid, such as air and passes through the conduit 14 to the device to belubricated such as bearings. lf there is an insufficient amount of oilsuspended in the air or an insufficient flow of the oil mist to thebearings, the bearings will not receive proper lubrication and will thusrapidly deteriorate.

In order to prevent such a problem, the monitoring apparatus 10 of theimmediate invention is connected with the mist supply 12. The monitoringapparatus 10 includes a density sensor 16 interposed between the mistsupply 12 and the bearings and a flow sensor I8 connected to the mistsupply 112. The density sensor 16 is electrically connected to a circuitmeans 20 to provide the circuit means 20 with signals, the difference ofwhich is proportional to the density of the mist flowing in the conduitI4, as will be described below. The flow sensor 18 is connected by lines22 to the circuit means 20 to provide the circuit means 20 with a signaldependent on the flow of the air entering the mist supply 112.Electrical power is supplied through line 23 to the circuit means inorder to power the monitoring apparatus as well known by those skilledin the art.

The circuit means 20 provides a Warning device 24 with a signal to alertan operator when the density of the mist or the flow of the mist dropsbelow apredetermined level as sensed by the density sensor I6 and theflow sensor 18, respectively. These predetermined levels may be adjustedby circuit-adjusting means 25, schematically indicated in FIG. 1.

The circuit means 20 also provides a dynamic signal to a densityindicator 26 and flow indicator 28 such that an exact indication of thedensity and flow of the mist is indicated respectively. Thus, when thewarning; signal is activated by either insufficient density or flow, anobserver may make an accurate analysis of the problem and adjust themist supply 12 correspondingly.

The density sensor 16 as shown in FIG. 2 includes a body 30 having apassageway 32 therein adapted to be interposed between portions of theconduit 14 such that the mist from the mist supply 12 flows through thepassageway 32 as it travels to the bearings. A' lamp 34 is mounted in anopening 36 in the body 30 and supplied with electrical power through theline indicated at 38. Light-restricting means 40 are provided torestrict and direct the light emitted by the bulb 34 through thetransparent plate 42 and into the passageway 32. In such a manner, lightis emitted into the passageway 32 such that mist will not be allowed tocontaminate the interior ducts 44. The ducts 44 are located in the bodyas hereinafter described for maintaining a blanket of clean airimmediately adjacent the light source 34 and light responsive means 54,72.

Since the intensity of the light given off by the light source 34 mayvary, a first sensor means 48 is provided in an aperture 50 which has anaxis common to the direction of light emitted by the light source 34through the light restricting means 40. A portion of the light soemitted, as represented by path 52, passes through the passageway 32without being reflected by the mist and is sensed by thelight-responsive means 54 after passing through the transparent plate56.

The transparent plate 56 is mounted in the aperture 50 such that sealingmeans 58 prohibits mist from entering the aperture 50 or the duct 44 andthus prevents contamination of the light-responsive means 54 which wouldprevent accurately sensing the intensity of the light source 34. Thephotocell 54 thus provides a signal proportional to the amount of lightemitted by the light source 34 and passing through the mist and throughthe restricting means 40. For example, when the density of the mistincreases or the intensity of the light source decreases, the signalfrom the first sensor means 48 will decrease. This signal is transmittedto the circuit means 20 by connecting lines 60. It should be understoodthat the first sensor 48 may be positioned in many other variouslocations that provide a difference between the signal from the firstsensor 48 and a second sensor 64 as hereinafter described.

Other portions of the light emitted by the light source 34 through thelight-restricting means 40 will be reflected by the mist asrepresentatively shown by path 62. A second sensor means 64 is providedto sense the amount of light so reflected and thus readily determine andprovide a signal proportional thereto. Such a second sensor means 64 ispositioned such that light reflected by the mist traveling in a commonplane to the light emitted from the light source 34, but not along thesame axis, will be sensed. For example, in an oil mist system, when thedensity of the oil 66 in the air 68 increases, the amount of lightreflected in path 62 will increase and thus signal from the secondsensor means 64 will proportionally increase. The second sensor 64detects the reflected light in path 62 through a transparent plate 70 bya light-responsive means 72, such as a photocell or phototransistors.The transparent plate 70 is provided with sealing means 74 to prohibitthe oil mist from entering the aperture 65 and consequently ducts 44which would contaminate them and prohibit an accurate signal from beingprovided to the circuit means 20. The light-responsive means 72 providesa signal proportional to the density of the oil mist to the circuitmeans 20 through lines 78. It should be apparent that the axes of thesensors 48, 64 and light source 34 are oriented in a radial directionwith respect to the apertu're 34 to maximize the operationalpredictability of such a system. In order to maximize the accuracy ofthis signal from the density sensor 16, the passageway 32 is paintedmatte black in order to prohibit light from being reflected therebytoward the sensor 64 as a result of reflection from the walls of thepassageway 32. It should be apparent that the light-responsive means 54,72 may consist of any light-responsive device such as a photocell orphototransistor.

Yet another solution to this wall reflection problem is variations inthe configurations of the walls. One such possible configuration isrepresentatively shown in a second embodiment of a density sensor inFIG. 3. For ease of description, corresponding numerals will be used forparts common to the designs shown in FIG. 2 and FIG. 3 with the commonpart shown in FIG. 3 having a suffix "a" after the correspondingnumeral.

The density sensor 160 as shown in FIG. 3, includes a light source 340which may be mounted as described in connection with FIG. 2, a firstsensor 48a, and a second sensor 64a. The passageway 32a has flat walls80 and 82, as shownin FIG. 3, such that light emitted from the lightsource 34a will not be reflected thereby and thus sensed by the secondsensor 64a. It is to be understood these walls 80 and 82 may take on amore complex form than shown in FIG. 3 to prohibit any light from beingreflected by the walls defining the passageway 32a. It should also beapparent that these walls 80, 82 defining aperture 32a may be painted ina matte black to further prohibit light from being reflected thereby.

The density sensor 16 and flow sensor 18 are connected to circuit means20 to activate a warning device 24 in a predetermined manner. FIG. 4shows the density sensor 16 schematically shown inside the dotted linesindicated 16, connected to the circuit means 20, enclosed by dottedlines generally indicated 20, to provide a signal proportional to thedensity of the mist contained in the conduit 14 to the circuit means 20.The flow sensor, shown schematically by the dotted lines generallyindicated 18, is connected to the circuit means 20 to provide a signaldependent on the flow of the fluid entering the mist supply 12. Thecircuit means 20 is adapted to supply the warning device 24 with asignal to activate the warning device 24 when the density of the mist orthe flow of the fluid drops below a predetermined level as hereinafterdescribed.

The density sensor 16 includes a light source 34 supplied with powerthrough lines 78 partially shown schematically in FIG. 4. Power will besupplied in the art and for ease of description, is not describedherein. The first sensor 54, schematically shown in FIG. 4, and thesecond sensor schematically shown at 72 is provided with a constantvoltage supply across points 96 and 98. These light-responsive sensors54 and 72 allow the current flow to increase as the light sensed therebyincreases which will result in a greater potential across points 98 and100 and 98 and 102 respectively.

Assuming that the intensity of the light source 34 remains constant whenthe density of the mist increases, the amount of light reflected willincrease such that the second sensor 72 will allow more current to flowthus increasing the potential between points 102 and 98. This increasein potential or signal will be received by the amplifier 104. Theamplifier 104 also receives a signal in a similar manner form the firstsensor 54. The signal from the second sensor 72 will be reduced by thesignal from the first sensor 54 by the differential amplifier 104. Thisdifferential signal is amplified by the amplifier 104 to provide anamplified differential signal of the density to a biased amplifier 122.It is to be understood that such a differential signal will have a widerange since the differential amplifier amplifies the difference in thesignals from the first and second sensors 54 and 72. Such an increasedrange improves the accuracy of such a monitoring apparatus and allowsthe output signal therefrom to be more sensitive to changes in density.For example, as the density of mist increases, the amount of lightreflected from the mist increases. Hence, the signal from the secondsensor 72 increases, and coincident therewith the light intensity whichis sensed by the first sensor 54 decreases due to the increase in mistdensity thereby establishing an enlarged difference between the signalsfor a given incremental change in mist density. It should be noted thata corresponding drop in the difference between the signals will occurwhen the density of the mist decreases.

To compensate for the varying intensity of the light source 34 and othersystem variables, the first sensor 54 will allow the potential betweenpoints 100 and 98 to increase as the light intensity increases;correspondingly, the second sensor 72 will allow the potential betweenpoints 102 and 98 to increase thus compensating for the intensitychange. It should be understood that the first sensor 54 may bepositioned in numerous positions to record the light intensity emittedby light 34 so that a resulting signal can be transmitted to thedifferential amplifier 104 concurrent with the signal being transmittedfrom the sensor 72 such that a differential signal is provided at theamplifier 104. For example, if the first sensor 54 was positioned tosense the intensity of the light directly and not across the mist, adifierential signal would be provided. However, the differential signalrange would not be as large as the range established by therelationships illustrated in FIG. 4. Circuit-adjusting means and 112 areprovided across points 100 and 98 and 102 and 98, respectively and maybe adjusted to initially balance the input to the amplifier l04 suchthat the amplifier 104 will give no output signal when no mist ispresent. Thus, the output signal of the amplifier 104 between terminals114 and 98 will be proportional to the density of the mist in theconduit 14.

A density indicator meter 26 is connected between points 114 and 98 toprovide a visible indication ofthe density of the mist in the conduit14. Adjusting means 116 is provided between point 100 and 114 to adjustthe gain of amplifier 104, thus adjusting the sensitivity thereof. Thisadjustment will allow an operation to compensate for the differentviscosities of the misting material misted.

A circuit-adjusting means 115 is provided between point 114 and theinput point 120 of a biased amplifier 122. The biased amplifier receivesthe amplified differential signal as modified by adjusting means 118 andis biased such that the amplified differential signal is furtheramplified thereby when it exceeds the biased level. The adjusting means118 is adjusted so that no output issues from amplifier 122 when themist density, decreases below a predetermined level. When the mistdensity, is above the predetermined level, the output of amplifier 122at point 124 will be above the biased level of the biased amplifier 122.A warning device such as a hell or a light schematically shown at 126,may be attached to point 124 to emit a signal when the density of themist drops below the predetermined level. Thus, the signal whichactivates the warning device is the lack of an output signal from biasedam plifier 122. It should be noted that a warning system that istriggered by the existence of a signal could also be utilized.

The flow sensor 18 consists of a first temperature-sensing means 90 suchas a thermistor, mounted in the fluid supply line 94 and a secondtemperature-sensing means 92, such as a thermistor, immediately adjacentto the fluid supply line 94 in the ambient air. Thermistor 90 senses thetemperature inside the fluid supply line 94 such that when fluid flows,the temperature of the thermistor 90 decreases. Consequently, itsresistance changes and creates a signal which may be sensed by thecircuit means 20. The thermistor 92 is used to compensate forfluctuations in the ambient air temperature and supply a signal to thecircuit means 20 proportional thereto. It should be noted that anyconventional flow sensor such as a pressure gauge could be used in theconduit line 14 or fluid supply line 94 to sense the flow of the fluid.ln order to provide a signal of the flow of the fluid, a constantpotential is applied between points 140 and 142. The potential betweenpoints 144 and 142 increases while the potential across points 140 and144 decreases as the flow increases, since the resistance of thermistor91) decreases.

When the flow decreases the resistance of the thermistor 90 increasesand the potential between points 144 and 142 decreases while thepotential between points 144 and 141) increases correspondingly. In asimilar fashion, the voltage across points 145 and 142 decreases as theambient air temperature increases due to the increase in resistance ofthe thermistor 92 and results in a voltage potential increase betweenpoint 140 and 145.

Thus, it may be seen that in operation as the flow increases, thetemperature of thermistor 90 decreases creating a corresponding voltageincrease between points 144 and 142. In a corresponding fashion, whenthe ambient temperature decreases, the thermistor 92 will create acorresponding voltage decrease between points 142 and 145.

The signal created by the thermistor 90 across points 144 and 142 andthe ambient temperature-compensating signal from thermistor 92 acrosspoints 145 and 142 is received by differential amplifier 143. Theamplifier 148 operates in a similar manner as hereinabove described inconnection with amplifier 104 and compensates for the ambient airtemperature with the signal from thermistor 92 and providesa signal atpoint 1511 which is dependent on the flow of the fluid in the fluidsupply line 94. This ambient temperature compensation is provided by theamplifier 148 by amplifying the difference between the signal from thecompensating sensor means 92 and the signal from the flow-sensor means91).

Circuit-adjusting means 152 and 154 are provided to adjust the inputsfrom points 144 and 145 respectively to the amplifier 148 such thatamplifier 148 is turned off when no fluid is flowing or the fluid flowhas dropped below a predetermined level. Thusthe circuit-adjusting means152, 154 may be used to provide a predetermined level above which asignal will be provided to indicate that fluid is flowing. A flowindicator meter 28 is provided and attached to the circuit means 20across points and 142. The flow indicator meter 28 thus provides avisible indication of the flow of the fluid. A circuitadjusting means156 is provided across points 142 and 150 to provide and AND-gate 160with a signal at point 162 when fluid is flowing through the fluidsupply line 94. The AND gate is also connected to point 124 and receivesa signal therefrom as hereinabove described.

When the AND gate receives a signal from both the density sensor 16 andflow sensor 18, the warning device 24 is activated. But when either thedensity sensor 16 or the flow sensor 18 does not provide a signal to theAND gate the AND gate provides a signal to the warning device thusactivating the warning device to alert the operator of the malfunction.For example, when the flow of the fluid drops below a predeterminedlevel, there will be no potential at point 162 and the warning device 24will be activated by a signal provided thereto by the AND gate. On theother hand, when the density of the mist in the conduit 14 drops below apredetermined level, there will be no signal at point 124 and thewarning device 24 will be activated by a signal provided thereto by theAND gate. Thus, when the density level and the flow indication are atthe proper level, inputs are furnished to the AN D- gate 161] and thewarning device 24 is not activated. But when either signal from point124 and 162, as hereinabove described drops below the predeterminedlevel, and the AND- gate will switch and activate the warning device 24.When the warning device 24 is activated, an observer may determine thespecific problem area by observing the mist density meter 26 and theflow indicator meter 28. It should also be noted that the mist-warningdevice 126 will be actuated when the mist density drops below apredetermined level to provide an additional feature to assure properlubrication of the aforementioned bearings.

It should be understood that the circuit means 20 could be attached tocontrol device which would automatically compensate for the varyingconditions of the mist system above described. It should be furtherunderstood that such a control device could be used in conjunction withthe warning device 24 as an additional safety precaution.

It should be apparent from the above that the present invention providesa monitoring apparatus for monitoring the presence of a material carriedby a fluid in a conduit and the flow of the fluid, comprising a circuitmeans adapted to receive a signal from a density sensor and a flowsensor which is dependent on the density and flow, respectively. Thecircuit means is adapted to activate a warning device when the flow orthe density drops below a predetermined level.

Having described my invention 1 claim:

1. An apparatus for monitoring the presence of a material carried by afluid in a conduit and the flow of said fluid comprising circuit meansfor indicating the density of the material carried by the fluid and theflow of the fluid, means for sensing the density of the material carriedby said fluid and operable to provide a first input signal to saidcircuit means dependent on said density of the material carried by saidflow of said fluid and operable to provide a second input signal to saidcircuit means dependent on said floe of fluid said circuit meansincluding means responsive to said first and second signals forproviding an output signal when said second signal from said means forsensing said flow indicates a flow below a first predetermined level orwhen said first signal from said means for sensing said density of thematerial drops below a second predetermined level or when said firstsignal from said means for sensing said density of the material dropsbelow a second predetermined level and warning means responsive to saidoutput signal for providing a warning signal to thereby indicate whenthe density of the material carried by the fluid is below said secondpredetermined level or the flow of the fluid is below said firstpredetermined level.

2. An apparatus for monitoring the presence of a material carried by afluid in a conduit and the flow of said fluid as defined in claim 1wherein said circuit means further includes first circuittadjustingmeans for varying said first predetermined level.

3. An apparatus for monitoring the presence of a material carried by afluid in a conduit and the flow of said fluid as defined in claim 2wherein said circuit means further includes second circuit-adjustingmeans for varying said second predetermined level.

4. An apparatus for monitoring the presence of a material carried by afluid in a conduit and the flow of said fluid as defined in claim 1wherein said means for sensing said density of the material carried bysaid fluid includes a light source adapted to providesaid conduit withlight, first sensor means for detecting light along a first path andproviding a signal proportional to the intensity of light in said onepath, second sensor means for detectinglight along a second path andproviding a signal proportional to the intensity of light in said secondpath, the first and second paths being such that said signal from saidsecond sensor means increases with respect to said signal from saidfirst sensor means as the density of the material carried by said fluidincreases, and comparator means for comparing said signal from saidfirst sensor means with the signal from said second sensor means, saidcomparator means providing said first input signal dependent on saiddensity of the material carried by said fluid.

5. An apparatus for monitoring the presence of a material carried by afluid in a conduit and the flow of said fluid as defined in claim 4wherein said second sensor means detects said light in said second pathby sensing the light provided by said light source which is reflected bysaid material.

6. An apparatus for monitoring the presence of a material carried by afluid in a conduit and the flow of said fluid as defined in claim 5wherein said means for sensing the flow of said fluid includes flowsensor means adapted to determine the flow of said fluid and operable toprovide a signal dependent thereon, compensating sensor means forproviding a signal for compensating for system variables, and means forcomparing said signals from said flow sensor means and said compensatingsensor means and operable to provide said second input signal dependenton said flow offluid.

7. An apparatus for monitoring the presence of a material carried by afluid in a conduit and the flow of said fluid as defined in claim 6wherein said means for comparing said signals from said flow sensormeans and said compensating sensor means is operable to determine thealgebraic difference between said signals from said flow andcompensating sensor means, said means for comparing said signals fromsaid flow sensor means and said compensating sensor means directing saidsecond input signal to said means responsive to said first and secondsignals to provide said output signal when said difference between saidsignals from said flow and compensating sensor means is ofapredetermined magnitude.

8. An apparatus for monitoring the presence of a material carried by afluid in a conduit and the flow of said fluid as defined in claim 6wherein said flow-sensor means includes a temperature changes created bythe flow of said fluid and said compensating sensor means including atemperature sensor for sensing the ambient air temperature of the airsurrounding said conduit.

9. An apparatus for monitoring the presence of a material carried by afluid in a conduit and the flow of said fluid as defined in claim 1including a density meter connected to said means for sensing thedensity ofthe material and responsive to said first input signal andoperable to give a visible indication of said density of the materialcarried by the fluid.

10. An apparatus for monitoring the presence of a material carried by afluid in a conduit and the flow of said fluid as defined in claim 9including a flow indicator connected to said means for sensing said flowof fluid and responsive to said second signal and operable to provide avisible indication of the flow of the fluid.

11. An apparatus for monitoring the presence of a material carried by afluid in a conduit and the flow of said fluid as defined in claim 1further including means responsive to said first input signal, adensity-warning device connected to said means responsive to said firstinput signal such that said density-warning device will be activated inresponse to said first input signal indicating said density of thematerial in said fluid is below said second predetermined level.

12. An apparatus for monitoring the presence of a material carried byfluid in a conduit as defined in claim I wherein said means for sensingthe density of the material includes light source means for directinglight into said conduit, first sensor means for detecting said light andproviding a signal proportional thereto, second sensor means fordetecting the amount of said light reflected by the material carried bysaid fluid and providing a signal proportional thereto, and comparatormeans for subtracting said signal from said first sensor means from saidsignal from said second sensor means and providing said first inputsignal, said means responsive to said first and second input signalsproviding said output signal when said first input signal drops below apredetermined level.

13. An apparatus for monitoring the presence of a material carried by afluid in a conduit as defined in claim 12 wherein said first sensormeans detects light along one path and provides said comparator meanswith a signal proportional thereto, said second sensor means detectslight along a different path and provides said comparator means with asignal proportional thereto, said paths being such that said signal fromsaid second sensor increases with respect to said signal from said firstsensor as the density of the material carried by said fluid increases.

14. An apparatus for monitoring the presence of a material carried by afluid in a conduit as defined in claim 13 wherein said first sensormeans is positioned along an axis common to the axis of said light.

15. An apparatus for monitoring the presence of a material carried by afluid in a conduit defined in claim 14 wherein said second sensor meansis positioned along an axis which is at an angle with respect to theaxis of said light such that the density of the material in said fluidis detected thereby.

16. An apparatus for monitoring the density of a material carried by afluid in a conduit as defined in claim 15 wherein said first sensorprovides said signal to said comparator means for compensating for theintensity of said light such that said first signal is not affected byfluctuations in the intensity of said light source.

17. An apparatus for monitoring the presence of a material carried by afluid in a conduit and the flow of said fluid comprising circuit meanshaving first amplifying means, light source means adapted to providesaid conduit with at least one ray of light in a substantially radialdirection with respect to said conduit, first sensor means for detectingsaid light and providing said first amplifying means with a signalproportional thereto, second sensor means for detecting said lightreflected by said material carried by said fluid and providing saidfirst amplifying means with a signal proportional thereto, said firstamplifying means adapted to provide a signal propor tional to saidsignal from said first sensor when subtracted from said signal from saidsecond sensor means, flow-sensing means adapted to detect the rate offlow of said fluid to provide a signal dependent on the rate of flow ofsaid fluid, and means responsive to said signals from said firstamplifying means and said flow-sensing means to provide an output signalwhen said density or said flow drops below a predetermined level.

18. An apparatus for monitoring the presence of a material carried by afluid in a conduit as defined in claim 17 wherein said circuit meansincludes a circuit-adjusting means for varying when said density dropsbelow said predetermined level.

I01 III II t I.

2. An apparatus for monitoring the presence of a material carried by afluid in a conduit and the flow of said fluid as defined in claim 1wherein said circuit means further includes first circuit-adjustingmeans for varying said first predetermined level.
 3. An apparatus formonitoring the presence of a material carried by a fluid in a conduitand the flow of said fluid as defined in claim 2 wherein said circuitmeans further includes second circuit-adjusting means for varying saidsecond predetermined level.
 4. An apparatus for monitoring the presenceof a material carried by a fluid in a conduit and the flow of said fluidas defined in claim 1 wherein said means for sensing said density of thematerial carried by said fluid includes a light source adapted toprovide said conduit with light, first sensor means for detecting lightalong a first path and providing a signal proportional to the intensityof light in said one path, second sensor means for detecting light alonga second path and providing a signal proportional to the intensity oflight in said second path, the first and second paths being such thatsaid signal from said second sensor means increases with respect to saidsignal from said first sensor means as the density of the materialcarried by said fluid increases, and comparator means for comparing saidsignal from said first sensor means with the signal from said secondsensor means, said comparator means providing said first input signaldependent on said density of the material carried by said fluid.
 5. Anapparatus for monitoring the presence of a material carried by a fluidin a conduit and the flow of said fluid as defined in claim 4 whereinsaid second sensor means detects said light in said second path bysensing the light provided by said light source which is reflected bysaid material.
 6. An apparatus for monitoring the presence of a materialcarried by a fluid in a conduit and the flow of said fluid as defined inclaim 5 wherein said means for sensing the flow of said fluid includesflow sensor means adapted to determine the flow of said fluid andoperable to provide a signal dependent thereon, compensating sensormeans for providing a signal for compensating for system variables, andmeans for comparing said signals from said flow sensor means and saidcompensating sensor means and operable to provide said second inputsignal dependent on said flow of fluid.
 7. An apparatus for monitoringthe presence of a material carried by a fluid in a conduit and the flowof said fluid as defined in claim 6 wherein said means for comparingsaid signals from said flow sensor means and said compensating sensormeans is operable to determine the algebraic difference between saidsignals from said flow and compensating sensor means, said means forcomparing said signals from said flow sensor means and said compensatingsensor means directing said second input signal to said means responsiveto said first and second signals to provide said output signal when saiddifference between said signals from said flow and compensating sensormeans is of a predetermined magnitude.
 8. An apparatus for monitoringthe presence of a material carried by a fluid in a conduit and the flowof said fluid as defined in claim 6 wherein said flow-sensor meansincludes a temperature changes created by the flow of said fluid andsaid compensating sensor means including a temperature sensor forsensing the ambient air temperature of the air surrounding said conduit.9. An apparatus for monitoring the presence of a material carried by afluid in a conduit and the flow of said fluid as defined in claim 1including a density meter connected to said means for sensing thedensity of the material and responsive to said first input signal andoperable to give a visible indication of said density of the materialcarried by the fluid.
 10. An apparatus for monitoring the presence of amaterial carried by a fluid in a conduit and the flow of said fluid asdefined in claim 9 including a flow indicator connected to said meansfor sensing said flow of fluid and responsive to said second signal andoperable to provide a visible indication of the flow of the fluid. 11.An apparatus for monitoring the presence of a material carried by afluid in a conduit and the flow of said fluid as defined in claim 1further including means responsive to said first input signal, adensity-warning device connected to said means responsive to said firstinput signal such that said density-warning device will be activated inresponse to said first input signal indicating said density of thematerial in said fluid is below said second predetermined level.
 12. Anapparatus for monitoring the presence of a material carried by flUid ina conduit as defined in claim 1 wherein said means for sensing thedensity of the material includes light source means for directing lightinto said conduit, first sensor means for detecting said light andproviding a signal proportional thereto, second sensor means fordetecting the amount of said light reflected by the material carried bysaid fluid and providing a signal proportional thereto, and comparatormeans for subtracting said signal from said first sensor means from saidsignal from said second sensor means and providing said first inputsignal, said means responsive to said first and second input signalsproviding said output signal when said first input signal drops below apredetermined level.
 13. An apparatus for monitoring the presence of amaterial carried by a fluid in a conduit as defined in claim 12 whereinsaid first sensor means detects light along one path and provides saidcomparator means with a signal proportional thereto, said second sensormeans detects light along a different path and provides said comparatormeans with a signal proportional thereto, said paths being such thatsaid signal from said second sensor increases with respect to saidsignal from said first sensor as the density of the material carried bysaid fluid increases.
 14. An apparatus for monitoring the presence of amaterial carried by a fluid in a conduit as defined in claim 13 whereinsaid first sensor means is positioned along an axis common to the axisof said light.
 15. An apparatus for monitoring the presence of amaterial carried by a fluid in a conduit defined in claim 14 whereinsaid second sensor means is positioned along an axis which is at anangle with respect to the axis of said light such that the density ofthe material in said fluid is detected thereby.
 16. An apparatus formonitoring the density of a material carried by a fluid in a conduit asdefined in claim 15 wherein said first sensor provides said signal tosaid comparator means for compensating for the intensity of said lightsuch that said first signal is not affected by fluctuations in theintensity of said light source.
 17. An apparatus for monitoring thepresence of a material carried by a fluid in a conduit and the flow ofsaid fluid comprising circuit means having first amplifying means, lightsource means adapted to provide said conduit with at least one ray oflight in a substantially radial direction with respect to said conduit,first sensor means for detecting said light and providing said firstamplifying means with a signal proportional thereto, second sensor meansfor detecting said light reflected by said material carried by saidfluid and providing said first amplifying means with a signalproportional thereto, said first amplifying means adapted to provide asignal proportional to said signal from said first sensor whensubtracted from said signal from said second sensor means, flow-sensingmeans adapted to detect the rate of flow of said fluid to provide asignal dependent on the rate of flow of said fluid, and means responsiveto said signals from said first amplifying means and said flow-sensingmeans to provide an output signal when said density or said flow dropsbelow a predetermined level.
 18. An apparatus for monitoring thepresence of a material carried by a fluid in a conduit as defined inclaim 17 wherein said circuit means includes a circuit-adjusting meansfor varying when said density drops below said predetermined level.